Color reproduction



g- I J. A. c. YULE 2,382,690

COLOR REPRODUCTION Filed April 1. 1942 /6. /A INCLfLZfiIi-F EEH fi B A Iv v MUL Tl COL 0R P08! 77 l/E OR NEGA T/VE WYELLON RED AND MASK NEGAT/VE OR POS/ TI l/E.

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SENSITIVE LAYER WITH YELLOW COUPLER.

L E LAYER WITH BLUE COUPLER.

SENSITIVE LAYER N/TH YELLOW COUPLER. D JENSIT IVE LAYER N/TH MAGENTACOUPLER.

gofglqlTll E LA YER WITH CYAN COUPLER.

LAYER N/THGREEN COUPLER. vE PART N/TH BLUE/0R MAGENTA COUPLERS.

GREEN 33-= AE-{GREENIIPART WITH YELLOW COUPLER. F 6 34", -REO PART wrmMAGENTA COUPLER.

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l 'f/HiTEi'L/fHT w 1 6 16 7/ 7 MULT/COLORED Po s/T/vE ION 0/? NEGATIVE.1

' MULT/COLORED MASK.

W I! 1% F I618 m ;{\w JOflNA gggg E MATERIAL e Patented Aug. 14, 1945 ICOLOR REPRODUCTION John A. C. Yule, Rochester, Eastman Kodak Company,corporation of New Jersey N. Y., assignor to Rochester, N. Y., a

Application April 1, 1942, Serial No. 437,156 29 Claims. (Cl. 95-2)based on.

separation" refers to that entity which is a component of the originaland which is recorded in various ways at various stages of the process.Manners of recording, distinguishing, correcting and otherwise operatingon the separations in the various known additive and subtractive colorprocesses are well understood. The present invention is particularlyapplicable to processes in which at least two primary color separationsmust be modified each in accordance with at least one primary colorseparation. This 18, of course, the phenomenon involved in the maskingmethod of color correction. The commonest examples of such processes arethose in which the final picture is made with subtractive coloringmaterials 01 which the magenta and cyan absorb some primary blue lightand the cyan absorbs some primary green light.

It is an object of the invention to provide a color correction in thoseprocesses in which a multicolored picture is made from a multicoloredrecord.

Specifically, it is an' object of the invention to provide a mask,preferably a universal mask, to be held in optical register with therecord while printing therefrom (e. g. while making color separationrecords or while printing onto a differentially sensitized multilayermaterial). The universal mask is one which remains in contact with therecord while all three separations are being printed eithersimultaneously or successively. Such a mask is a decided advantage evenwhen making distinct color separation records because of the difflcultyof registering individual masks.

It is the primary object of the invention to provide a. universal maskwhich gives better color correction than previous universal masks. Amask according to the present invention not only gives to an improveddegree thetype of color correction available with previous masks butalso tends to correct for any hue errors in the final printing dyes orinks.

A short review of the more recent types of universal masks will aid inthe understanding of the present invention. Copending application337,300, Hanson, filed May 25, 1940, now U. S. Patent 2,294,981,describes the preferred method of making a. neutral universal mask (thatis, it is fundamentally neutral though it may be colored monochromouslyas described in application 413,442, Evans, filed October 3, 1941). Sucha neutral mask corrects for the absorption of blue .and red by themagenta used in the final print and for the absorption of blue and greenby the cyan so used. If the hues of these final coloring materials areright (e. g. ii the red and blue absorptions by magenta are exactlyequal), such a neutral mask gives the maximum correction and even withshifted hues, Hansons method gives the best possible neutral mask. TheEvans monochromous mask the Hanson type of masking to correct forimproper color gammas either in the original record or in thereproduction process, still apparently assuming proper hues.

One of the special advantages and objects of the present invention isrection of this usual masking type, it also tends to correct forimproper hues. Hence, it is especially useful in photo-mechanicalprocesses wherein it is desirable, for the sake of improved brightnessesin the reds, to employ reddish magentas (so-called process red) and forthe sake of improved purity in blues, violets and purples, to employbluish rather than blue-green cyans (so-called process blue) even thoughtheir hues are definitely ofi. On the other hand, practically everyprocess has some hue errors and, hence, the present invention findsgeneral application.

The present invention is employed in a process for making multicolorpictures from a multicolor record. The process may be eitherphotomechanical or photographic such as when using difierentiallysensitized multilayer materials. The multicolor record may be anythingcolored and if it is a photograph it may be a positive or a negative andmay be produced subtractively 0r additively. Most commonly, it is asubtractive positive or negative transparency made on multilayermaterials but it may be a real optical image projected from lenticularfilm through proper filters or it may be a screen record, in which casethe mask should be made suillciently diffused to obliterate the screenpattern, or a painting, or even a still-life subject. However, theinvention will be described with reference to a transparency.

According to the invention the record is modijust referred to, modifiesthat in addition to corfied so that exposures therethrough will be colorcorrected, 1. e. a universal mask is provided for the record. .To dothis, a sensitive material is placed in printing relation, preferably bycontact but possibly by projection printing, to the record,

which material is made up of separate parts order to get colorcorrection, the part whose exposure corresponds to the primary colorseparation which is to do the modifyin ris processed to a color whichabsorbs the primary color corresponding to the separation which is to be-modi-.

fied. This mask is then held in optical register, preferably in contactwith the multicolored record when printing separation negatives oranother multilayer material therefrom. For example, when the blue andgreen separations must be modified respectively in accordance with thegreen and red separations, a sensitive material is used for the mask inwhich one part is'sensitive to green light and another part is sensitiveto red light and after exposure the green sensitive part is processed toa color which absorbs blue and the red sensitive part to color whichabsorbs green, in order to get the color correction required.Furthermore the red sensitive part is processed to a color which alsoabsorbs red so as to reduce the red contrast to match the blue contrast.Therefore in the preferred form of the invention, the red sensitive partis processed to primary blue. In practice, when the red sensitive partis processed to blue either directly or in two portions, one to magentaand the other to cyan, the resulting blue absorbs some blue itself sothatthe blue separation is also modified to some extent by the red. Theextent of this depends on the purity of the green and red absorbers.

In one embodiment of the invention the green sensitive part is processedto yellow so that the green separation modifies only the blueseparation, and in another embodiment it is processed to green so thatthe green separation modifies both the blue separation and the redseparation.

The relative advantages of these two types of color correction are wellunderstood by those familiar with the various ramifications of themasking theories In these examples I have found that approximately theright degree of color correction is given when both parts are processedto effectively equal gammas. Furthermore, such an arrangement has anadvantage when processing to yellow and blue respectively since if thesecomplementary colors are processed to equal equivalent games, a grayscale such as is often incorporated into or mounted adjacent to themulticolor record being copied, my duces as neutral ay and thus providesan accurate check on the processing of the mask. Any shift in colorbalance involving improper gammas of the records can be corrected inlater stages of-the process by reducing or increasing the game. of oneparticular separatiom On the other hand, certain photo-mechanicalprocesses usually require relatively reduced contrasts for the yellow(blue), and magenta (green) separations, which contrasts are normallycontrolled by varying the lens aperture or the distance of the halftonescreen. To eliminate the need for this type of control, the yellow andmagenta in the mask may be developed to a gamma higher than the cyan.This trick applies when the blue part of the mask is produced in twoportions, one of which is cyan and the other magenta, but the sameeffect may be produced when a single blue dye is used by the use of apurplish blue. In fact, one of the most satisfactory methods ofproducing this mask is to use a multilayer material having three layers,one of which is sensitive to green and the other two of which aresensitive to red, and which layers contain couplers so that the greensensitive layer is developed to yellow or green, and the red sensitivelayers are developed respectively to cyan and magenta having equalequivalent gammas or galmnas which differ by the small amountreferred toabove. Also' the present invention is not limited to the method in whichthe green sensitive part of the material is processed to a coloredimage. Since equal equivalent gammas of the three subtractive colors addto gray, the term equivalent gamma refers to the gamma of the gray scaleequivalent to the color scale being measured. When a gray scale, exposedto neutral light and processed to a substantially neutral gray, has agamma of one, the individual color components each have an equivalentgamma of one, although their absolute values are less than one as iswell known. The conversion factor from absolute gamma to equivalentgamma is constant for each color. Equivalent gamma is a term pertinentonly to 2 or 3 colors which are mutually complementary because summationto gray is obviously involved: it is, however, quite a useful propertyin such complementary systems.

The processing of the mask may be done separately and then the maskreregistered with the original or the mask may be processed in situ.

. In this latter case, the masking material may be provided with anadhesive and possibly also with a protective layer to protect theoriginal record from the processing solutions. The material is placed incontact with the record, exposed through the record, processed, andwhile'it is still in contact with the record, color separation negativesor a color print is made therefrom.

In the case where the green sensitive part is processed to green, I havefound that it is desirable to use a light somewhat more deep orange thanred when printing the red separation from the corrected' record. Also inthis case where the green sensitive part is processed to green, I havefound that it is advantageous to process the red sensitive part tomagenta or at least to a blue which transmits red light somewhat morethan usual. In all cases, however, the green sensitive part is processedto a color which absorbs blue and transmits green and the red sensitivepart is processed Just oppositely t absorb green and transmit blue.

Whatever form of multicolored record is being printed, the mask alwayshas a density negatively proportional to the density of the record,meassured with respect to appropriate primary colors. Thus, if themulticolored record is a positive, the mask is a multicolored negative,and if the record is a negative, the mask is a positive.

As is common practice when discussing dyes, the terms transmit" and"absorb are used only relatively meaning transmit to a high degree" or"absorb to a high degree" since no dye absorbs or transmits any colorcompletely.

The invention, its objects, advantages. and the principles involved,will be understood from the following description when read inconnection with the accompanying drawing in which:

Figs. 1A to 1E illustrate the making of color separation recordsaccording to the invention.

Fig. 2 shows one form of material for making a multicolor mask accordingto the invention.

Figs. 3 to 7 illustrate various forms of multilayer material useful formaking masks according to the invention.

Fig. 8 illustrates printing onto a multilayer material according to theinvention.

In Fig. 1A a multicolored record Iii which may be either positive ornegative and is provided with a support H is to be used for making colorseparation negatives or positives. For this purpose a sensitive materialI2 carried on a support i3 is placed in printing relation to the recordl specifically in contact therewith. The material I! is made up of partsdifierentially sensitive to red and green and is exposed asindicated byarrows i4 through the record I0 by light including red and green. Thenas indicated by the arrow ii the green sensitive part is processed toyellow or green and the red sensitive part is processed to blue. Asshown in Fig. 1B the multicolor record it is now masked by a multicolormask it which is negative with respect to the record, i. e. is negativeif the record is positive, and is positive if the record is negative.This universal mask I6 is held in contact with the record I0 while thered, green, and blue separations are made therethrough as indicated byarrows l7 onto sensitive materials ll of ap- Serial No. 814,689, Mannesand Godowsky, now U. 8'. Patent 2,304,940. Useful couplers, specificallya green coupler, are also described in U. 8. 2,126,337, Marines andGodowsky. A copending application filed concurrently herewith relates tothe materials I prefer to use for making the masks.

In Fig. 4 the red sensitive part is made of two layers 30 and 3|, one ofwhich contains the magnets coupler and the other of which contains thecyan coupler. In Fig. the red sensitive part is all in one layer 21which contains a blue coupler or which contains both magneta and cyancouplers and the green sensitive part 32 propriate sensitivity andcarried on supports ll.

As is well known, the separations may be exposed by monochromatic red,green, and blue light. In

the embodiment wherein the green sensitive part of the material I! isprocessed to green, I prefer to use a somewhat orange light for theprinting of the red separation, but this is not critical to the presentinvention. V

In Fig. 2 the sensitive material i2 is provided with a thin support 2!and on the rear surface of the support with an adhesive 22 so ,that itmay be fastened permanently to the record ll and remain in contacttherewith during processing and subsequent printing. The support 2i mayalternatively be thick if a diffuse mask is desired as described in mycopending application filed.

The diiierentially sensitive parts oi! the material i2 may beincorporated therein in any known manner, but I prefer to use amultilayer material as illustrated in Figs. 3 to'7. In Fig. 3 thesupport l3 carries three layers, the top one of which is a yellow filter25 to cut 05 blue light and the second and third layers are respectivelya green sensitive one 26, and a red sensitive one 2i. Since these layersare to be processed directly to negatives with respect to the exposinglight, I prefer to provide the color development by means of couplers inthe layers. As is known, couplers are usually those compounds having areactive methylene group or phenolic hydroxyl group and which couplewith the development product of a primary aromatic amino developingagent. of course, the present invention is not limited to this detail.Examles of such couplers are given in copending application 371,612,Jelley contains a green coupler. In Fig. 6 the green sensitive part IIis provided with a yellow coupler and the red sensitive part is providedwith a magneta coupler in layer 34 and the mask then does not balancethe red contrast which therefore is corrected separately in later steps01' the process. In Fig. 7 the green sensitive part It is provided witha yellow coupler as before and the red sensitive part I! is providedonly with a cyan coupler so that the blue and green separations aremodified by the red separation only to g the extent in which the cyanunavoidably absorbs the blue and green. In general, this latterembodiment provides correction of blue by green and the correction ofred by red to control contrast only and is not preferable since itprovides no correction oi green by red which is important in present dayprocesses.

a In Fig. 8 the multicolor record II is provided I with a multicolormask I! while printing onto a multilayer material 4| carried on asupport ll. If the multicolor record I! is a positive, the mask I shouldbe a negative and the multilayer ma,- terial ll may be processed byreversal to a positive. On the other hand, if the record II is anegative and the mask II is a positive, the layer 4. should be processeddirectly so as to give a positive. The color correction is, of course,for errors in the spectral distribution of absorption by the dyes usedin the layer I in this case.

Having thus described the preferred embodiments of my invention, I wishto point out that it is not limited to these arrangements but is of thescope of the appended claims.

What I claim and desire to secure by Letters Patent 01 the United Statesis:

1. In a process for making a subtractive multicolored picture from amulticolored record in which process at least two primary colorseparations must be modified each in accordance with at least onediil'erent primary color separation by factors equivalent to theunwanted absorptions of the primary color in each case by the coloringmaterial complementary to said diflerent primary color used in makingsaid muticolored picture, the method of modifying the record whileprinting therefrom so that exposures made therethrough will be colorcorrected and Vittum, now U. S. Patent 2,322,027, and in 15 correctedand to approximately equal to the corresponding unwanted absorptionfactors and printing from the multicolored record a color separation ofeach primary color-while holding said mask in optical register to therecord.

2. .In a process for making a subtractive multicolored picture from amulticolored record in which-process the blue and green separations'must be modified in accordance with the green and red separationsrespectively by factors proportional to theblue and green'absorption bythe magneta and cyan materials used in making the multicolored picture,the method'of modifying the record while printing therefrom so thatexposures made therethrough will be color corrected which methodincludes the steps of placing in printing relation to the record amaterial having at each point one part which is sensitive. t greenlightand another part which is sensitive to red light, exposing saidparts through the record to light including red and green, processingthe material to a multicolored mask for the record by processing saidparts to differently 7 colored images negative to the record, the greensensitive part being processed to a color which absorbs blue and to agamma approximately equivalent to the blue absorption factor of themagneta material to be used in making the multicolored picture and .thered sensitive part being processed to a color which absorbs green and toa gamma approximately equivalent to the green absorption factor of thecyan material used in making said multicolored record, and printingfromthe multicolored record a color separation of each primary .colorwhile holding said mask in optical register with the record.

3. The method according to claim 2 in which I. the red sensitive part isprocessed to blue whereby it also absorbs red.

4. A method according to claim 2 in which the green sensitive part isprocessed to yellow and the red sensitive part is processed to blue.

5. A method according to claim 2 in which the green sensitive part isprocessed to green and the red sensitive part is processed .to magenta.

6. A method according to claim 2 in which the green sensitive part isone layer of the material and. is processed to yellow and the redsensitive part is two other layers of the material, one of which isprocessed to cyan and the other of which is processed tomagenta.

'7. A method according to claim 1 in which said parts are processed toequivalent gaanmas which are eflectively equal to each other and thecolors of the differently colored images are complementary whereby agray area in the record gives a gray area in the mask.

8. A method according to claim 2 in which said parts are processed toequivalent games which are effectively equal to each other and thecolors tary whereby a gray area in the record gives a gray area in themask.

9. The method according to claim 1 in which said printing of the colorseparations is success ve.

10. The method according to claim 1 in which said printing of the colorseparations is simultaneous and onto a multilayer differentially colorsensitized material.

11. The method according to claim 1 in which thematerial is placedsubstantially in contact with the record and remains in contact durinzneous and onto a multilayer diflerentially color sensitized material.

14. The method according to claim 2 in which the material is. placedsubstantially in contact with the record and remains in contact duringsaid exposing, processing, holding, and printing.

15. The method of making color corrected color separation negatives froma multicolored positive which comprises placing in printing relation tothe positive a material having at each point part which is sensitive togreen light and part which is sensitive to red light, exposing thematerial through the positive to light including red and green,processing the material to a subtractively multicolored negative maskfor the positive by processing said parts to diiierently colorednegative images, the green sensitive part being processed to a colorwhich absorbs blue and to a gamma approximately equivalent to the blueabsorption factor of magenta. materials used in a subtractive colorreproduction process and the red sensitive part being processed to acolor which absorbs green and transmits blue and to a gamma saidexposing, processing, holding, and printing.

17. The method of making color corrected color to separation negativesfrom a multicolored positive of the differently colored images arecomplemenwhich comprises placing in printing relation to the positive amaterial having at each point part which is sensitive, to green lightand part which is sensitive to red light, exposing the material throughthe positive to light including red and green, processing the materialto a subtractively multicolored negative mask for the positive byprocessing said parts to differently colored nesa-' tive images, thegreen sensitive part being processed to a color which absorbs blue andtransmits green and to a gamma approximately equivalent to the blueabsorption factor of magenta materials used in a subtractive colorreproduction process and the red sensitive part being processed to acolor which absorbs green and transmits blue and to a gammaapproximately equivalent to the green absorption factor of cyanmaterials used in the reproduction process and printing each of thethree primary color separations from the positive while holding the maskin optical register therewith.

18. The method according to claim 17 in which the green sensitive partis processed to yellow. 19. The method according to claim 1'1 in whichthe green sensitive part is processed to green and of the three primarycolor separation negatives the red one is printed with deep orangelight.

20. The method according to claim 17 in which the green sensitive partis processed to yellow and the red'sensitive part to blue and both partsare processed to equivalent gammaswhich are eil'ec-' 15 the sensitivepart is made of two portions one of which is processed to cyan and'theother to magenta and in which the green sensitive part is processed toyellow, the processing to yellow and magenta being to an equivalentgamma slightly and appreciably higher than that to which the cyan isprocessed.

22. The method according to claim 17 in which the material is placedsubstantially in contact with the record and remains in contact duringsaid exposing, processing, holding, and printing.

23. For use in a color reproduction process in which at least twoprimary color separations must be modified each in accordance with atleast one other primary color separation by a factor equivalent to theunwanted absorption of each primary color respectively by the coloringmatetractively multicolored mask in register therewith said mask havingat each point yellow and blue parts, the density of the yellow part toblue light being negatively proportional to the green density of thetransparency and the density of the blue part to green light beingnegatively proportional to the red density of the transparency,

the proportionality factors being respectively those required for colorcorrection in a subtractive color reproduction process.

25. The combination of a multicolored positive transparency and auniversal negative subtractively multicolored mask having at each pointreen transmitting and green absorbing parts,

the density of the green transmitting part to blue light beingnegatively proportional to the green density of the transparency and thedensity of the green absorbing part to green light being negativelyproportional to the red density of the transparency, the proportionalityfactors being respectively those required for color correction in a.subtractive color reproduction process.

26. In a process for making a subtractively multicolored picture from amulticolored record in which process at least two primary color recordsmust be modified each in accordance with .at least one different primarycolor separation by factors equivalent to the unwanted absorption of theprimary color in each case by the coloring material complementary tosaid diiferent primary color used in math. laid multicolored picture,the method of modifying the record which comprises placing in printingrelation to the record a material having at each point separate partswhich are sensitive to light of said different primary colors, exposingsaid parts through the record to light including said different primarycolors, processing the parts to differently colored images negative tothe record and, to gammas approximately equalivent to the correspondingunwanted absorption factors, to forma subtractively multicolored maskfor the record and printing three primary color separation records fromthe record and mask held in optical register.

27. The method according to claim 26 in which the material isplacedsubstantially in contact with the record and remains in contactduring said exposing, processing, and printing.

28. The method according to claim 26 in which said printing of the colorseparations is succes- .sive.

29. The method according to claim 26 in which said printing of the colorseparations is simulo taneous and onto a multilayer differentially colorsensitized material.

JOHN A. 0. mar.

